The pathogenicity of twenty-seven British isolates of Phytophthora fragariae Hickman to strawberry varieties and seedlings is described and nine physiologic races are characterized by the response of Huxley Giant, Perle de Prague, Redgauntlet, Talisman, Siletz and an Auchincruive seedling 52AC18. The relationship between these races and those described by Hickman is examined and a classification of British races suggested. Tests of the pathogenicity of American and Canadian races are described and the results related to the British classification.